1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a record medium, the image forming apparatus including a record-medium determining apparatus that determines a type of the record medium by irradiating modulated light on the record medium and detecting intensity of reflected light of the light.
2. Description of the Related Art
In order to perform high-quality image formation in image forming apparatuses such as a copying machine and a printer, it is necessary to adjust a printing method to a type of a record medium such as a sheet on which an image is formed. For example, when an image is printed on plain paper and when an image is printed on an OHP sheet, a high-quality image is not obtained unless the printing method is adjusted to the plain paper and the OHP sheet.
An operator manually selected a type of a record medium in models at the initial stage. However, since the operator sometimes makes mistakes in the selection, apparatuses that detect types of sheets have been developed.
In the conventional technique, an apparatus is proposed which reflects light of one LED light source on a sheet and detects reflected light of the light with optical sensors provided in a regular reflection direction and a diffuse reflection direction. (E.g., JP-A-2005-75469).
This apparatus determines a type of a sheet by changing a quantity of light of the LED light source and comparing the reflected light detected by the respective optical sensors with a threshold set in advance.
However, in this technique, there is a problem in that, when light other than the light of the LED light source is present, since this light is made incident on the optical sensors as noise, it is impossible to determine a type of the sheet.
Moreover, the technique has a problem in that it is necessary to lead a sheet set as a reference into the image forming apparatus and perform calibration in order to compare the reflected light with the threshold, resulting in a burden on an operator.